Clinical progress in the treatment of primary tumors has been slow and one of the problems associated with these tumors is their weak response to anticancer drugs. The effectiveness of chemotherapy and immunotherapy have been impaired by inherent or acquired multiple drug resistance (MDR) phenotype by cancer cells. One mechanism involved in MDR phenotype is caused by the expression of P-glycoprotein (P-gp), a membrane transporter that pumps out various anticancer drugs from MDR1 expressing cells. P-gp is also expressed in a large number of normal secretory tissues such as kidney, liver and intestine. This efflux pump is strongly expressed in the brain capillaries where its expression was mainly localized in the luminal membrane of endothelial cells lining these. In human, P-gp is encoded by two MDR genes; MDR1 and MDR3. P-gp encoded by the human MDR1 gene confers the resistance phenotype whereas P-gp encoded by the human MDR3 gene does not. Thus, P-gp may be seen as a guardian that limits the entry of drugs by expulsing them out of the brain or out of cancer cells preventing them from reaching cytotoxic concentrations.
Cancer cells forming brain metastases originate mostly from lung or breast cancers, colorectal carcinoma, melanoma and urinary organ tumors. These metastases, which often occur after surgery, primary chemotherapy treatment or radiotherapy, are chemo-resistant. Chemotherapy against brain metastases could be effective only if it was effective for their corresponding originate tumors. For example, it was shown that brain metastases originating from small cell lung carcinomas and germ cells respond with similar rates than metastases at other sites.
Drug resistance may be an intrinsic property of tumor cells or may be acquired after treatment. The presence of the P-gp efflux pump encoded by MDR1 (also herein referred as P-glycoprotein, MDR1 P-gp or MDR1) has been reported in most of the primary brain tumors where most gliomas and more particularly endothelial cells of newly formed capillaries were stained positive for MDR1 P-gp. Thus, various studies support the idea that the multiple drug resistance phenotype may be caused not only by the expression of P-gp in cancer cells but also from its expression in the newly formed endothelial cells in the tumors. MDR1 levels were also found significantly lower in brain metastasis from melanomas and lung adenocarcinomas. In addition, it was shown that treatments prior to surgery have no major impact on MDR1 levels in brain metastasis from melanomas since they were identical in patients that received radiotherapy, chemotherapy or both treatments. In lung metastasis, MDR1 was only detected in patients that received chemotherapy indicating that these previous treatments may have induced its expression resulting in an acquired MDR phenotype. The lack of MDR1 expression in primary lung tumors and in their corresponding brain metastasis indicates also that these metastases did not acquire the same levels of P-gp expression during their development than the ones found in normal brain tissue. These results also indicate that the MDR1 levels of endothelial cells from capillaries in brain metastasis differed from the one of primary brain tumors. The lack of MDR1 expression in some brain metastasis may explain in part why some of them are more sensitive to chemotherapeutic drugs than primary brain tumors.
Methods for transporting a compound across the blood-brain barrier have been described in international application no. PCT/CA2004/000011 published on Jul. 22, 2004 under publication No. WO2004060403, the entire content of which is incorporated herein by reference. Briefly, in this document, aprotinin, aprotinin fragments and analogs were presented as a drug delivery system for the central nervous system (CNS) and for treating CNS related diseases.
There remains a need for increasing the potency of anticancer drugs.
The present invention seeks to meet these and other needs.